The present invention pertains to a new and improved form of a non-pneumatic tire of the type used on vehicles having narrow rims such as bicycles, wheel chairs and the like and to a process of preparing the same which allows for proper placement of a bead cord within the beads of the tire.
The typical type of bicycle tire on the market is a pneumatic tire which is constructed much like an automobile tire having a cord carcass and steel wire embeded within the beads of the tire. This type of tire requires the use of a tube since the tire rim has plurality of spokes attached to the rim which inhibits the use of a tubeless type tire. For light weight bikes used in cross-country riding and in racing a tire is used which requires a tube to be laced within a very light weight tire. This racing type tire suffers from the same type of disadvantages outlined below for the common tire in addition to it being very time consuming and tedious to lace the tube within the tire.
The disadvantages of pneumatic bicycle tires include safety hazards due to blowouts and punctures as well as very poor service life due to relatively thin treads. The thin treads contribute to the safety hazard in that they are easily punctured by common sharp objects found in the roads, such as nails or glass and further they even can be damaged by sharp stones.
With increasing cost consciousness the quality of the tubes used in the common bicycle tire, such as that found on a child's bicycle, has decreased and typically at the junction where the stem of the tube is molded to the tube leakage of air can occur. To combat this leakage of air it is necessary to either carry a tire pump to keep the tires properly inflated or continually make trips to a service station to inflate the tire with compressed air.
There have been attempts to overcome some of the above outlined disadvantages by filling the tire with a urethane resin in place of an inflatable tube. This requires filling the tire with a mixture of two components which react within the tire to form a solid resilient elastomeric body within the tire. This type of tire filling has been used successfully for automobile tires. This approach has been used with bicycle tires and tires filled with urethane do eliminate problems such as blowouts, slow leaks and underinflation, but they create a new problem in regards to weight. A typical urethane filled bicycle tire will weigh up to five or six pounds per tire making a total weight penalty to up to ten pounds for the bicycle. Since the bicycle is propelled by pedal power, weight is considered a grave disadvantage. A bicycle enthusiast thinks of his tires in terms of minimum ounces or grams and not in terms of pounds or kilograms. A further disadvantage of a urethane filled tire is that the ride is harder and the rolling resistance is increased. Ride comfort and rolling resistance are mutually antagonistic quantities. Attempts to maximize one of these properties results in jeopardizing the other and it is usually necessary to make a compromize between them.
Once a tire is filled with urethane forming resins which react or cure to form a solid body within the tire it is almost impossible to remove the tire from the wheel rim for spoke repairs or adjustments because not only does the tire have to be removed from the rim but it also has to be removed from the solid urethane body which was formed between the tire and the rim. Normally removal of a tire in a case such as this is impossible without actually cutting the tire and destroying it. An advantage of a tubed tire and a disadvantage of a solid urethane filled tire is the distribution of stress upon impact of the tire against a sharp object. The tubed tire can distribute this stress wherein the solid filled tire cannot and the stress is therefore transmitted to the wheel rim damaging it.
Recently, efforts have been made to develop a solid, monolithic type of urethane elastomer having a tunnel on the inside to allow the tire to compress under impact loads. However, this has proved to be a difficult thing to achieve, as a tire made of a urethane soft enough to give a comfortable ride, turns out to have unsatisfactory resistance to wear and cuts, while urethane hard enough to give good resistance to wear and cuts gives a hard, uncomfortable ride.
One of the more difficult problems with a solid, monolithic tire of urethane elastomer having a tunnel on the inside, is the tendency of the tires to come off the rims, even though they are glued to the rim with an adhesive. This is due, in part, to the fact that the only thing holding the tire bead shoulders against the rim is the adhesive bond, which is frequently less than perfect owing to the difficulty of getting a uniform film of adhesive on the mating surfaces. Another contributing factor is the elasticity of the unreinforced elastomer, which allows the tire to stretch under certain loading conditions. The problem is particularly acute when a side thrust is applied to the tire, as when cornering or bumping against a curb or simply turning the wheel when the tire is not rolling as when a rider is stopped waiting for a traffic light or other such instance.